1. Field of the Invention
The present invention generally relates to a magneto-generator (also known as the magnetoelectric generator) for generating electric energy or electricity under the action of electromagnetic induction taking place between magnets mounted on a flywheel and an armature winding during rotation of the flywheel. More particularly, the present invention is concerned with an improved structure of a guard annulus or ring which is employed for protecting and positioning a plurality of magnets mounted on an inner peripheral surface of the flywheel.
2. Description of Related Art
For having better understanding of the concept underlying the present invention, description will first be made of a conventional flywheel type magneto-generator by reference to FIGS. 7 and 8 of the accompanying drawings, in which FIG. 7 is a front view of a rotor of a conventional flywheel type magneto-generator which is disclosed, for example, in Japanese Patent Publication No. 81437/1994 (JP-A-6-81437), and FIG. 8 is a section view of the same taken along the line VIII-VIII shown in FIG. 7 and viewed in the direction indicated by arrows. Referring to the figures, a rotor of the magneto-generator includes a flywheel 11 implemented in a substantially bowl-like shape (hereinafter also referred to as the bowl-shaped flywheel only for the convenience of description). On the inner peripheral wall of the flywheel 11, four magnets 12 each having an arcuate cross-section are fixedly mounted with equidistance between adjacent ones in the circumferential direction. A guard annulus or ring 13 of a substantially cylindrical shape is tightly or closely fit onto the inner surfaces of the magnets 12 which are disposed in a substantially annular array. Further, resin 14 is filled at both sides and between the adjacent ones of the magnets 12 for fixedly securing the magnets 12 and the guard ring 13 integrally to the flywheel 11. Furthermore, a hub or boss 15 is formed in the flywheel 11 at a center portion of the bottom wall thereof for coupling the rotor to a rotatable shaft (not shown).
In the rotor of the conventional magneto-generator implemented in the structure described above, the four magnets 12 are disposed with equidistance therebetween on the inner peripheral surface of the flywheel 11 with the guard ring 13 of the cylindrical shape being tightly fit onto the magnets 12 on the inner side thereof, wherein the voids or spaces defined between the inner peripheral surface of the flywheel 11 and the outer peripheral surface of the guard ring 13 are filled with the resin 14. In this manner, the magnets 12 and the guard ring 13 are fixedly secured to the flywheel 11 by the resin 14. The guard ring 13 is provided for the purpose of protecting the plurality of magnets 12 mounted on the inner peripheral wall of the flywheel 1 from being injured when these magnets 12 strike against other objects under the magnetic force upon handling of the rotor.
FIG. 9 is a perspective view showing another example of the guard ring employed in the conventional magneto-generator, and FIG. 10 shows the same partially in section in the state in which magnets are disposed on the guard ring shown in FIG. 9. As can easily be seen in FIG. 9, the guard ring 13 shown in this figure is designed to be employed in the magneto-generator in which a large number of magnets 12 are used with the width thereof in the circumferential direction being reduced when compared with the rotor shown in FIG. 8. As can be seen in FIGS. 9 and 10, the guard ring 13 is generally of a cylindrical shape and formed with a plurality of retaining portions 13a each having a substantially C-like section with equidistance therebetween in and along an opened peripheral edge portion of the ring 13 located at the bottom side of the flywheel 11. On the other hand, formed in the opened peripheral edge portion located oppositely to the retaining portions 13a is a flange 13b. The inner peripheral surface of the guard ring 13 serves for positioning the magnets 12 in the radial direction, while the positions of the magnets 12 in the rotational axis direction (i.e., in the direction along the axis of the rotatable shaft (not shown)) are fixed or delimited by the retaining portions 13a and the flange 13b between which the magnets 12 are sandwiched, as can clearly be seen in FIG. 10.
The guard ring 13 can be manufactured by punching a non-magnetic sheet material such as, for example, a stainless sheet into a predetermined shape or pattern by means of a pressing machine, forming the retaining portions 13a each of C-like cross-section by cutting and bending one end portion while forming the flange 13b by bending vertically the other edge portion. Subsequently, the steel sheet is rounded into a body of cylindrical shape, whereon the abutting end portions of the sheet rounded cylindrically are joined together by welding.
In the magneto-generator of the structure described above, an annular generator coil (not shown) is disposed internally of the flywheel 11 around the boss 15. In other words, the generator coil is so disposed as to face toward the annular array of the magnets 12 with the guard ring 13 being interposed therebetween. In operation, magnetic fluxes emanating from the magnets 12 run through the iron core of the generator coil, whereby electricity is generated.
However, the conventional magneto-generator of the structure described above suffers a problem that due to interposition of a thick wall portion of the guard ring 13 between the magnet array (12) and the generator coil, the air gap defined between the magnet array and the generator coil is effectively enlarged when the rotor rotates around the outer periphery of the generator coil (not shown) because the guard ring 13 is made of a non-magnetic material, as mentioned previously. As a result of this, efficiency or effectiveness of the magnetic fluxes emanating from the magnet array (12) and running through the iron core of the generator coil becomes lowered, incurring degradation in the efficiency of electricity generation of the magneto-motor.
Certainly, the problem mentioned above can be coped with to certain extent by employing the thin guard ring 13. In that case, however, another problem may arise that the flange 13b which should intrinsically extend radially outwardly at 90 degrees relative to the rotational axis is likely to be bent at an angle a greater than 90 degrees, as illustrated in FIG. 11, or undergo undesired deformation such as corrugation, which makes it difficult or practically impossible to position correctly and positively the magnet array (12) in a satisfactory manner.